"The downgrade is based on our concerns with deteriorating motorcycle demand," said S&P credit analyst Andy Liu.

Milwaukee-based Harley has been facing falling sales as pinched consumers cut back on purchases of its high-end, highly discretionary motorcycles. Earlier in July, the company said its second-quarter profit plummeted 91 percent, with U.S. retail sales falling 35 percent. Harley also announced another 1,000 job cuts.

"We believe that Harley-Davidson sales could be down as much as 30 percent in 2009," Liu said.

Shares of Harley rose 2 cents to close Monday at $21.76. The stock has traded from $7.99 to $48.05 in the last 52 weeks.